This invention relates to engine cooling systems for vehicles, such as trucks, cars or buses, as well as stationary generator units, in particular to cooling systems provided with an expansion tank closed to the ambient atmosphere.
Engine cooling systems of this type often comprise an expansion tank. The expansion tank has many functions, among them to take care of the coolant expansion caused by increased coolant temperature, and to build up pressure in the system in order to pressurize the coolant pump suction side to avoid pump cavitation. For a truck or stationary engine installation with a coolant system containing 50-70 liters the coolant may expand around 2 liters from cold start to normal working temperature.
With expansion tanks used in vehicles today, a common solution is to use a controllable valve that may be set to open at a predetermined, relatively high pressure. The valve links the expansion volume inside the expansion tank with ambient air. This means that when the coolant is heated and expands, the air in the expansion tank is compressed until the pressure reaches the higher setting of the valve. The valve opens and releases air to the ambient atmosphere until the pressure has dropped to a desired pressure. This air is saturated with coolant, which is lost to the ambient air.
GB 1049771 A describes a system closed to the ambient comprising an air big enough that a pressure release valve is unnecessary. Such systems require big air volumes or sufficiently small coolant volumes.
Pressurized coolant systems are disclosed in US 20050061264 A1, U.S. Pat. No. 6,666,175 B2, and GB 931087 A.
The system of US 20050061264 A1 continuously adds new oxygenated air to the expansion tank (and the coolant) and continuously relief air which is saturated with vapor from the coolant through the relief valve to the atmosphere in order to control the pressure. U.S. Pat. No. 6,666,175 B2 discloses that the compressor supplies compressed air to the compensating tank.
During operating conditions when the temperature of the coolant is reduced, for example due to lower engine load or the cooling fan starting to engage, the coolant volume decreases and the pressure at the pump will be lowered. This will in turn reduce the pressure of the air in the expansion tank. When this pressure drops below a lower setting of the valve the valve opens, letting ambient air into the tank. This prevents the pressure in the cooling circuit from dropping below a predetermined pressure where cavitation may occur in the coolant pump.
It is desirable to solve at least one of the above discussed problems associated with prior art coolant systems, and particularly to provide a cooling system that can be controlled to quickly build up pressure at the coolant pump suction side when starting the engine, in order to avoid cavitation in the pump.
The invention relates, according to an aspect thereof, to an engine cooling system. The invention also relates, according to another aspect thereof, to a vehicle provided with such an engine cooling system.
The invention relates, according to an aspect thereof, to an engine cooling system with a cooling circuit comprising a coolant pump for supplying an engine with a coolant and for circulating the coolant in the cooling circuit and at least one heat exchanger for cooling said coolant downstream of the engine. In the cooling circuit, the pump will supply coolant to the engine, wherein the coolant is heated. Heated coolant may pass through a thermostat which, depending on the temperature of the coolant, will direct the coolant directly back to the pump or to a heat exchanger. The heat exchanger may be a radiator arranged to reduce the temperature of the coolant to a desired level. An expansion tank may be connected to the cooling circuit upstream of the coolant pump. The cooling system is pressurized by a pressure regulating means arranged to pressurize coolant supplied to the cooling circuit from the expansion tank during at least one predetermined operating mode of the engine and the expansion tank is closed to the ambient atmosphere during all normal engine operation modes. For instance, one such operating mode may be a cold start of the engine.
Pre-pressurizing the coolant supplied to the coolant pump reduces the risk of cavitation in said pump, due to a relatively low pressure in the suction conduit when the engine is started. Furthermore, by such an engine cooling system an even pressure without pressure peaks (high and low pressure) can be maintained. This is an advantage because pressure peaks may cause damage to the components of the coolant system. Introduction of ambient air into the system and loss of coolant to ambient air can be avoided, and thus oxidation of the coolant is prevented or counteracted.
According to a first embodiment, the pressure regulating means is located in the expansion tank and may be arranged to displace a volume of coolant in the expansion tank. When the pressure regulating means is pressurized, the pressure of the coolant in the expansion tank increases and the pressurized coolant will be forced into a suction conduit for the pump in the cooling circuit. The pressure regulating means may be a diaphragm or a similar suitable device arranged in the expansion tank. The system may be pressurized by increasing the volume of such a diaphragm by supplying it with compressed air or a similar suitable fluid. The system pressure is controlled by a suitable valve, such as a 3-way valve, that can either let air into the expansion tank or release it to the ambient air. The function of such a valve will be described in further detail below. The expansion tank may further contain a pressure actuated safety valve that will open to ambient air if the pressure in the tank increases above a predetermined maximum allowed pressure.
The volume of the expansion tank is preferably relatively large. A large expansion tank may contain a comparatively large diaphragm that may be used to create a desired pressurization of the coolant over a relatively large span of temperatures and coolant volumes. Also a relatively large expansion tank allows excess pressure to escape from the cooling circuit without causing an undesirably high pressure in the said tank. In a standard size tank, excess pressure spikes may cause a safety valve to open, which in turn would result in an undesired release of air and coolant to the ambient atmosphere. The volume of the expansion tank may be selected in the range 10-30%, preferably about 15%, of the total system volume. For the most common engine sizes, the volume of the expansion tank may be selected in the range 25-40 liters, depending factors such as the total cooling circuit volume and desired coolant pressure to be delivered to the suction conduit of the pump.
The pressure regulating means may be supplied with a pressurized fluid from an external source of pressure. The external source of pressure may be compressed air from a tank or compressor adjacent the engine or on a vehicle on which the engine is mounted. The source of compressed air could for example be supplied by an existing brake compressor in the vehicle or from an air compressor in a supercharged engine. Other suitable pressure sources may be pressurized hydraulic fluid from a pump on or adjacent the engine. Such a compressor or pump may be driven by the engine or a similar suitable source of power.
As the pressurized fluid is contained in a volume separated from the coolant, the fluid and the coolant are maintained in a non-contacting relationship to avoid contamination of the coolant. The fact that the cooling system is not directly connected to ambient air means that no coolant will be lost to the ambient air, and that no air that can oxidize the coolant will be introduced in the cooling system.
In a first example of the first embodiment, the expansion chamber may be located on the heat exchanger upstream of the coolant pump. For instance, if an upper section of the radiator is the highest located point of the cooling circuit, then the expansion tank may be mounted on or adjacent the upper section of said radiator. In this example, the expansion tank will also act as a deaeration chamber, wherein gas bubbles may be removed from the coolant.
In a second example of the first embodiment, the cooling system may comprise a separate deaeration chamber located at the highest point of the coolant system upstream of the coolant pump. The deaeration chamber may be mounted on the heat exchanger or radiator arranged to cool the coolant. The volume of the deaeration chamber may be relatively small and is mainly used to deaerate the system and to provide a location for filling coolant. For instance, when using an expansion tank with a volume of about 30 liters, the volume of the deaeration chamber may be in the range of 0.5 liters. However, even when using a large expansion tank with a volume around 40 liters, the volume of the deaeration chamber should preferably not exceed 5 liters. Similar to the first example, the gas may escape to the deaeration chamber through conduits connected to the thermostat and the upper tank of the radiator. A lower section of the deaeration chamber is connected to the suction conduit of the pump, in order to provide a static fill for the cooling circuit. An upper section of the deaeration chamber is in turn connected to a lower section of the expansion tank. This allows excess pressure to escape the cooling circuit by passing from the deaeration chamber into the expansion tank. Also, pressurized fluid may be forced from the expansion tank, through the deaeration chamber and into the suction conduit of the pump, in order to allow pressurization of the coolant supplied to the pump.
By providing the deaeration chamber on or adjacent the upper section of the radiator, the expansion chamber may be placed remote from the radiator. This allows the expansion tank to be placed in any suitable location on the truck, for example on the frame or chassis of a vehicle. Locating the expansion tank on the frame or chassis of the vehicle also adds to the packaging flexibility of the expansion tank. The smaller deaeration chamber can more easily be packaged on top of the cooling package, or radiator and the larger expansion tank can be placed in any suitable location. Furthermore, the larger expansion volume allows the same parts to be used on a wider range of installations.
As stated above, in connection with the first and second examples, the pressure regulating means may be connected to a source of fluid pressure via a controllable valve. The valve may be a pressure controlled valve that can be controlled by the pressure in the expansion tank. The valve may be a pressure controlled valve actuated directly by the pressure in the expansion tank, or a solenoid valve actuated on the basis of a signal from a pressure sensor in the tank.
The cooling system pressure may preferably, but not necessarily, be controlled by a pressure actuated 3-way valve. During start-up of the engine the valve may be arranged in an open position, in order to pressurize a diaphragm in the expansion tank to a predetermined pressure using a source of pressure. The valve may be maintained in a first open position as long as the pressure in the expansion tank is less than a predetermined pressure setting for the valve. When the pressure in the cooling circuit and the expansion tank reaches the set pressure for the valve, the valve will move to a closed position in order to maintain this pressure. The pressure setting for the valve may be a substantially fixed pressure or a range comprising an upper and a lower limit at which limits the valve is arranged to switch. During normal operation of the engine after start-up, the valve is controlled by the pressure in the expansion tank to maintain a predetermined pressure in the expansion tank and the cooling circuit. If a pressure spike, higher than the desired set pressure, should occur in the cooling circuit, the increased pressure may act on the valve to move it to a second open position to release pressure from the diaphragm. Should the cooling circuit experience a pressure cycling relative to the pre-set pressure for the valve, the valve may be used to counteract this condition. During each pressure drop the valve may be moved to the first open position to supply pressure to the diaphragm, while a subsequent increase in pressure may cause the valve to be moved to the second open position to release pressure from the diaphragm.
The expansion tank may also be provided with a safety valve. The safety valve may be set to release a relatively high excess pressure to the atmosphere. The valve release pressure is preferably set at a level that will maintain the cooling system in a closed state during all normal operating conditions. The valve should only open when there is a risk of damaging components in the cooling system. The safety valve is preferably, but not necessarily, a pressure controlled 2-way valve. The valve is normally maintained in a closed position, but may open at a predetermined set pressure to release excess pressure from the expansion tank.
According to a second embodiment, the pressure regulating means may be located in a supply conduit connecting the expansion tank to the cooling circuit system upstream of the coolant pump, hereinafter referred to as the main coolant pump. The cooling system may comprise a separate deaeration chamber located at the highest point of the coolant system upstream of the main coolant pump. The deaeration chamber may be mounted on the heat exchanger or radiator arranged to cool the coolant. The volume of the deaeration chamber may be relatively small and is mainly used to deaerate the system and to provide a location for filling coolant. For instance, when using an expansion tank with a volume of about 30 liters, the volume of the deaeration chamber may be in the range of 0.5 liters. However, even when using a large expansion tank with a volume around 40 liters, the volume of the deaeration chamber should preferably not exceed 5 liters. Any gas present in the coolant may escape to the deaeration chamber through conduits connected to the thermostat and the upper tank of the radiator. A lower section of the deaeration chamber is connected to the suction conduit of the pump, in order to provide a static fill for the cooling circuit. An upper section of the deaeration chamber is in turn connected to the expansion tank. In this embodiment the cooling system may comprise a deaeration chamber located upstream of the main coolant pump. The expansion tank is connected to the deaeration chamber via a conduit provided with a controllable valve. The controllable valve is preferably, but not necessarily, a pressure controlled 2-way valve. The valve can be spring loaded towards a closed position, but may open when the pressure in the main cooling circuit exceeds a predetermined set pressure to release excess pressure from the deaeration chamber to the expansion tank, in order to maintain a desired pressure in the main cooling circuit. When the engine is running a pre-pressurizing pump may be operated continuously to supply the main circuit with pressurized coolant. The pressure in the main circuit is maintained and controlled by the pressure controlled valve located between the deaeration tank and the expansion tank.
By providing the deaeration chamber on or adjacent the upper section of the radiator, the expansion chamber may be placed remote from the radiator. This allows the expansion tank to be placed in any suitable location on the truck, for example on the frame or chassis of a vehicle. Locating the expansion tank on the frame or chassis of the vehicle also adds to the packaging flexibility of the expansion tank. The smaller deaeration chamber can more easily be packaged on top of the cooling package, or radiator and the larger expansion tank can be placed in any suitable location. Furthermore, the larger expansion volume allows the same parts to be used on a wider range of installations.
As in the first embodiment above, the volume of the expansion tank is preferably relatively large. A large expansion tank may be used to allow a desired pressurization of the coolant over a relatively large span of temperatures and coolant volumes, without having to vent the tank to the ambient atmosphere during periods of relatively high pressure in the system. The volume of the expansion tank may be selected in the range 10-30% of the total volume of the cooling system. The volume of the expansion tank may be selected in the range 25-40 liters, depending factors such as the total cooling circuit volume and desired coolant pressure to be delivered to the suction conduit of the pump.
According to the second main embodiment of the invention, the pre-pressurized coolant is supplied by the pre-pressurizing coolant pump as previously described, or alternatively by any other suitable pressure regulating means, such as for example an injector device. During certain operating conditions, such as a start-up of the engine, the pump may draw coolant from the expansion tank and supply pre-pressurized coolant to the main coolant pump in the cooling circuit. This reduces the risk of cavitation in the main coolant pump, due to a relatively low pressure in the suction conduit when the engine is started.
The system pressure may be controlled by the pressure controlled valve using a signal from a pressure sensor located at a suitable position in the cooling circuit, such as immediately upstream of the main coolant pump. During start-up of the engine the pre-pressurizing coolant pump may be arranged to supply coolant from the expansion tank at a predetermined pressure to the main coolant pump. When the pressure in the cooling circuit and the expansion tank reaches the set pressure the pre-pressurizing coolant pump is continuously operated to assist the main coolant pump in maintaining a predetermined pressure in the cooling circuit. During normal operation of the engine after start-up, the pressure controlled valve is opened or closed to maintain this pressure. If a pressure spike, higher than the desired set pressure, should occur in the cooling circuit, the increased pressure may act on the controllable valve to move it to an open position. Excess pressure will then be released from the deaeration chamber to the expansion tank. Should the cooling circuit experience a pressure cycling relative to the pre-set pressure for the cooling circuit, the pre-pressurizing coolant pump and the controllable valve may be used to assist the main coolant pump in counteracting this condition. During each pressure drop the pre-pressurizing coolant pump will supply pressure to the suction conduit to counteract this condition, while a subsequent increase in pressure may cause the controllable valve to be moved to its open position to release pressure to the expansion tank.
Alternatively, the pre-pressurizing coolant pump may be operated as long as the pressure in the suction conduit is less than a predetermined pressure. When the pressure in the cooling circuit and the expansion tank reaches the set pressure the pre-pressurizing coolant pump is deactivated, where after the main coolant pump will maintain this pressure. During normal operation of the engine after start-up, the pre-pressurizing coolant pump may be controlled by a sensed pressure in the expansion tank to assist the main coolant pump in maintaining a predetermined pressure in the cooling circuit. If a pressure spike, higher than the desired set pressure, should occur in the cooling circuit, the increased pressure may act on the controllable valve to move it to an open position. Excess pressure will then be released from the deaeration chamber to the expansion tank. Should the cooling circuit experience a pressure cycling relative to the pre-set pressure for the cooling circuit, the pre-pressurizing coolant pump may be used to assist the main coolant pump in counteracting this condition. During each pressure drop the pre-pressurizing coolant pump may, if necessary, be actuated to supply pressure to the suction conduit, while a subsequent increase in pressure may cause the controllable valve to be moved to its open position to release pressure to the expansion tank.
The volume of the expansion tank is preferably relatively large. A large expansion tank may contain a comparatively large diaphragm that may be used to create a desired pressurization of the coolant over a relatively large span of temperatures and coolant volumes. Also a relatively large expansion tank allows excess pressure to escape form the cooling circuit without causing an undesirably high pressure in the said tank. In a standard size tank, excess pressure spikes may cause a safety valve to open, which in turn would result in an undesired release of air and coolant to the ambient atmosphere. The volume of the expansion tank may be selected in the range 25-40 liters, depending factors such as the total cooling circuit volume and desired coolant pressure to be delivered to the suction conduit of the pump.
The expansion tank may also be provided with a safety valve. The safety valve may be set to release a relatively high excess pressure to the atmosphere. The valve release pressure is preferably set at a level that will maintain the cooling system in a closed state during all normal operating conditions. The valve should only open when there is a risk of damaging components in the cooling system. The safety valve is preferably, but not necessarily, a pressure controlled 2-way valve. The valve is normally maintained in a closed position, but may open at a predetermined set pressure to release excess pressure from the expansion tank. An additional sensor can be located in the expansion tank for monitoring the pressure therein and/or to control a solenoid operated safety valve.
The invention further relates to a vehicle provided with a cooling system as described for the first and second embodiments above. Hence the vehicle may be provided with a pressure regulating means arranged to displace the coolant in the expansion tank, by means of a diaphragm or similar, using a source of fluid pressure via a controllable valve. The pressure source may be an air tank, an air compressor or a compressor in a supercharger located on vehicle.
Alternatively the vehicle may be provided with a pressure regulating means for maintaining a predetermined pressure in the main coolant pump, as described above. The pressure regulating means may be a controllable pump or an injector arranged to supply coolant under pressure to the main coolant pump in the cooling circuit. This arrangement may be used to prevent cavitation in the main coolant pump during certain operating conditions, such as a start-up of the engine.
The pressurized cooling systems described in the above embodiments provide a cooling system that can be controlled to quickly build up pressure at the coolant pump suction side when starting the engine, in order to avoid cavitation in the pump. The pressurized cooling systems according to the invention also provides means for maintaining an even pressure that is high enough to avoid pump cavitation during operation of the engine, even when the coolant has cooled down. The cooling systems also make it possible to avoid pressure peaks (high and low pressure) and pressure cycling that may damage the components in the coolant system. It is also desirable to avoid introducing ambient air into the system, which air may oxidize the coolant (ageing of coolant), and to avoid loosing coolant to ambient air. The invention will therefore have a positive effect on the life time of the components in the coolant system and of the coolant and the efficiency of the coolant pump. Examples of additional advantages with the solutions according to the invention are that coolant top off intervals should be less frequent since there is no continuous loss of coolant, which is also beneficial for the environment. Since the expansion tank has a larger expansion volume which is less sensitive to small leaks. With the expansion tank mounted on the chassis, the tank is easier to service and facilitates reading of the coolant level.